Because of the standard height of tunnels and overhead power wires, many double-decker trains set the bottom deck lower down between the bogies. At the entrance platforms of the train there is just a single deck, above the bogies. From there one can go upstairs or downstairs. For example, for the DD-IRM (see below) it is one step up from the station platform to the entrance platform, and from there 7 steps up or 4 steps down.
Other double-decker trains, however, such as those using rolling stock made by Colorado Railcar Manufacturing[?], house the entrance on the lower deck rather than an intermediate level. The Amtrak Superliners[?] are also double-decker trains of this variety, housing the entrance about a step or so up from the (generally low) platform of the railroad stations, and allowing passage from car to car through the upper corridors of the train. (Colorado Railcar Manufacturing, responsible for constructing the Princess cars on the Alaska Railroad[?], can be located online at  (http://www.coloradorailcar.com/).
In some countries such as the United Kingdom the railway system cannot accommodate double decker trains because the loading gauge[?] is to small (i.e. bridges, tunnels, etc. are too low). An intermediate form of two-level seating arrangement has been tried in Britain, where the bottoms of the upper seats are above the heads of the people on the lower level, but the feet of the people above are not, see  (http://members.tripod.com/~dart75/bddscut.htm).
There are double-decker trams in Hong Kong.
See also: transport.